Conventional throttle valve control systems for motor vehicles exist in which the throttle valve opens in direct proportion to the depression of an accelerator pedal. A problem with this design is that often times it is desirable to decrease the sensitivity of the vehicle's accelerator pedal when operating at low speeds, for instance when one is attempting to maneuver in a cramped position. In order to attain some type of non-linear ratio between depression of the accelerator pedal and position of the throttle valve, designers have generally employed complex multi-lever linkages. For example, U.S. Pat. No. 4,782,805 to Kawano and U.S. Pat. No. 4,476,068 to Griffin disclose multiple lever throttling devices in which continued depression of the accelerator pedal results in an increasingly larger incremental opening of the throttle valve. U.S. Pat. No. 4,450,807 to Kinoshita discloses a similar device in which the rate at which the throttle valve opens decreases with pedal travel. A drawback to these designs, however, is that they require a spring on one or more of the ratio-obtaining secondary levers, i.e. those levers that are not directly attached to the throttle shaft, or a bar between the primary and secondary levers, to ensure that the entire linkage returns fully to the idle position. The presence of additional springs or bars on the interconnecting levers often duplicates the effort of a spring attached to the primary lever, but is necessary to reduce any initial free play in the system that otherwise results from slack between the levers. Alternative designs such as U.S. Pat. No. 4,779,480 to Stocker, assigned to the assignee of the present invention, disclose mechanisms which achieve variable ratios through the use of a pivot point of relative rotation between throttle linkage levers which is not fixed. This arrangement, however, also results in the situation where initial depression of the accelerator pedal does not result in instantaneous throttle response.